1. Field of the Invention
The present invention relates to projection type image display apparatus for color separating illumination light to illuminate a plurality of image display devices with the separated light components and combining image light components emanating from these image display devices for projective display.
2. Description of the Related Art
In recent years, a projection type image display apparatus with an improved brightness and a compact size is needed.
FIG. 4 shows the configuration of a conventional projection type image display apparatus. In FIG. 4, white illumination light emitted from an illumination light source 101 is reflected by a reflector 102, passes through a fly eye lens 103, further reflected by a mirror M101, passes through a fly eye lens 104, a light polarization converting device 105 and a condenser lens 106, and then incident on a dichroic mirror DM101.
In general, as the illumination light source, a halogen lamp, a metal halide lamp, an ultra-high pressure mercury lamp or the like is used.
The dichroic mirror DM101 has a spectral transmittance shown in FIG. 5(a), in which a light component in a wavelength range for blue is reflected and a light component in a wavelength range for green to red is transmitted. The light component in the wavelength range for green to red passing through the dichroic mirror DM101 is incident on a dichroic mirror DM102. The dichroic mirror DM102 has a spectral transmittance shown in FIG. 5(b), in which a light component in a wavelength range for green is reflected and a light component in a wavelength range for red is transmitted.
The light component in the wavelength range for blue reflected by the dichroic mirror DM101 is turned 90 degrees by a reflecting mirror M102, passes through a field lens 107B, and incident on an image display device 108B, where the light is modulated in accordance with a signal input to the image display device 108B.
The light component in the wavelength range for green reflected by the dichroic mirror DM102 passes through a field lens 107G and is incident on an image display device 108G, where the light is modulated in accordance with a signal input to the image display device 108G.
The light component in the wavelength range for red transmitted through the dichroic mirror DM102 passes through a trimming filter TRO having a spectral transmittance shown in FIG. 5(c), a condenser lens 111, a relay lens 112, reflecting mirrors M103, M104 and a field lens 107R, and then is incident on an image display device 108R, where the light is modulated.
The image light component for each color, modulated by the respective image display device 108R, 108B and 108G as described above, is incident on a cross dichroic prism 109. The light components in the wavelength ranges for blue and red are turned 90 degrees within the cross dichroic prism 109, while the light component in the wavelength range for green is transmitted as it is through the cross dichroic prism 109. Then, the light components of all the wavelength ranges emanate in combination.
The image light resulting from the color combination in the cross dichroic prism 109 is projected and displayed on a screen, not shown, by a projection lens 110.
In the conventional projection type image display apparatus configured in this manner, the dichroic mirror DM102 is disposed immediately before the image display device 108G and is responsible for separating the optical path of the light component in the wavelength range for green from the optical path of the light component in the wavelength range for red and for bending the optical path of the light component in the wavelength range for green. The dichroic mirror DM102 is arranged such that the optical axis of the light incident on the dichroic mirror DM102 forms an angle of 45 degrees with the normal to the incident surface of the dichroic mirror DM102.
In the aforementioned configuration of the apparatus, however, the optical axis of the illumination light from the illumination light source 101 to the reflecting mirror M101 is arranged in parallel with the optical axis of the projection lens 110, and the condensing effect of the condenser lens 106 converges the luminous flux toward the image display device 108R, 108G and 108B. Thus, when the apparatus is housed in an outer box 120, the probability is that spaces S1, S2 with little usefulness are created as shown by hatched portions in FIG. 6 to increase the apparatus in size.
In addition, while the aforementioned image display apparatus employs the relay lens 112, the reflecting mirrors M103, M104 and the like to form the relay system for red light, it is contemplated that a relay system formed of combined concave mirrors is used instead of the above relay system. The concave mirrors, however, are likely to suffer from aberration if light is incident thereon at a large angle, thereby possibly causing loss of light quantity or failing to achieve favorable display images.